A vehicle drivetrain transfers motive power from a power source to vehicle wheels. An engine is one example of a power source that includes a crankshaft. The crankshaft converts combustion energy from engine cylinders into rotational energy. In particular, combustion energy is transferred from the engine cylinders to pistons that linearly reciprocate. The pistons transfer the combustion energy to a crankshaft via rods, and the crankshaft converts the linear motion into rotational motion. The crankshaft may also include main bearing journals that are in mechanical communication with crankshaft bearings. The crankshaft bearings are captured between an engine block and the crankshaft. Lubrication flows from the engine block to the bearings, and the engine block supports the bearings and the crankshaft. The engine block and bearings allow the crankshaft and main bearing journals to rotate within the bearings. One example crankshaft is disclosed in U.S. Patent Publication No. 2005/0115524 which shows a four cylinder engine having five main bearings rotatably coupled to a crankshaft in the engine. The bearings guide crankshaft rotation and are mechanically coupled to an engine block that supports the crankshaft and bearings.
A crankshaft may flex as torque is input to the crankshaft via connecting rods. Crankshaft flex may limit engine speed and increase engine vibration. One way to reduce crankshaft flexing is to provide a large number of main bearing journals along the length of a crankshaft so that the crankshaft can be supported at many locations. However, engine friction losses are proportional to a number of crankshaft bearing journals. Therefore, engine friction losses increase for each crankshaft bearing journal that is added to a crankshaft. As a result, the engine's power output and fuel economy may be substantially decreased as the number of bearing journals increase. Moreover, engine weight is increased for every additional crankshaft bearing journal. Consequently, engine block cost increases as a number of crankshaft main bearing journals increases.
To address at least some of the aforementioned issues an inline four cylinder engine, comprising: a crankshaft including two outer main bearing journals and a sole inner main bearing journal axially positioned between the two outer main bearing journals is provided. Thus, an inline four cylinder engine including only three main bearings is provided.
By limiting a number of main bearings of an inline four cylinder engine to three rather than the customary five, it may be possible to reduce engine friction and improve vehicle fuel economy. In one example, the engine includes three main bearing saddles with bearings that guide and support a crankshaft with three main bearing journals. A first bearing journal is positioned at a front side of the crankshaft, a second bearing journal is positioned at a rear side of the crankshaft, and a third bearing journal is positioned near a middle of the crankshaft. In this way, the crankshaft may be sufficiently supported while engine friction is reduced.
The engine and crankshaft described herein may reduce engine fuel consumption. Further, the engine and crankshaft may vibrate and/or flex less than other designs. Further still, the engine and crankshaft may operate efficiently at higher engine speeds.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings. It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.